[PATCH] Fix ICE with widen_mult and -ftrapv (PR tree-optimization/83523)

[Jakub Jelinek]

Hi!

Converting widening mult, or widen_{plus,minus}_expr, or integral mult to
fma is IMNSHO undesirable with -ftrapv for signed types - the expansion of
those doesn't detect overflows and by giving up we don't need to worry about
formerly trapping MULT_EXPR becoming something that isn't trapping and
performing EH cleanups etc.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2017-12-21  Jakub Jelinek  <ja...@redhat.com>

        PR tree-optimization/83523
        * tree-ssa-math-opts.c (is_widening_mult_p): Return false if
        for INTEGER_TYPE TYPE_OVERFLOW_TRAPS.
        (convert_mult_to_fma): Likewise.

        * g++.dg/tree-ssa/pr83523.C: New test.

--- gcc/tree-ssa-math-opts.c.jj 2017-12-21 09:43:19.000000000 +0100
+++ gcc/tree-ssa-math-opts.c    2017-12-21 12:22:10.576488270 +0100
@@ -2196,8 +2196,12 @@ is_widening_mult_p (gimple *stmt,
 {
   tree type = TREE_TYPE (gimple_assign_lhs (stmt));
 
-  if (TREE_CODE (type) != INTEGER_TYPE
-      && TREE_CODE (type) != FIXED_POINT_TYPE)
+  if (TREE_CODE (type) == INTEGER_TYPE)
+    {
+      if (TYPE_OVERFLOW_TRAPS (type))
+       return false;
+    }
+  else if (TREE_CODE (type) != FIXED_POINT_TYPE)
     return false;
 
   if (!is_widening_mult_rhs_p (type, gimple_assign_rhs1 (stmt), type1_out,
@@ -2656,7 +2660,7 @@ convert_mult_to_fma (gimple *mul_stmt, t
 
   /* We don't want to do bitfield reduction ops.  */
   if (INTEGRAL_TYPE_P (type)
-      && !type_has_mode_precision_p (type))
+      && (!type_has_mode_precision_p (type) || TYPE_OVERFLOW_TRAPS (type)))
     return false;
 
   /* If the target doesn't support it, don't generate it.  We assume that
--- gcc/testsuite/g++.dg/tree-ssa/pr83523.C.jj  2017-12-21 12:20:56.555403891 
+0100
+++ gcc/testsuite/g++.dg/tree-ssa/pr83523.C     2017-12-21 12:20:02.000000000 
+0100
@@ -0,0 +1,25 @@
+// PR tree-optimization/83523
+// { dg-do compile }
+// { dg-options "-O2 -fexceptions -fnon-call-exceptions -ftrapv" }
+
+#ifdef __SIZEOF_INT128__
+typedef __int128 T;
+typedef long long int U;
+#else
+typedef long long int T;
+typedef int U;
+#endif
+
+struct S { S (); ~S (); };
+void bar ();
+
+T
+foo (U x, U y)
+{
+  T z = x;
+  S s;
+  bar ();
+  z *= y;
+  bar ();
+  return z;
+}

        Jakub